The present invention relates to a power distribution system which can be mounted in various vehicles including motor vehicles, and more particularly to a power distribution system for distributing and supplying electric power to various electric loads in a vehicle.
As an example of conventional vehicles, a motor vehicle in which a 14-V output power supply unit having an alternator and a rechargeable 12-V battery is mounted (i.e., a so-called 14-V vehicle) is known. A power distribution system which is applied to this 14-V vehicle is comprised of a junction box for receiving the power supply of a high voltage (e.g., 14 V) from the power supply unit, as well as a plurality of electronic control units electrically connected to this junction box through a plurality of power lines. Incorporated in each electronic control unit is a series regulator which receives the high-voltage power distributed from the junction box through a power line. In this power distribution system, the electric power of a high voltage in the junction box is converted to electric power of a low voltage (e.g., 5 V) by each series regulator which functions as a voltage converting unit, and the electric power of the low voltage thus converted is supplied to a plurality of electric loads which are electrically connected to each electronic control unit.
In recent years, development of high-voltage vehicles in which a power supply unit with a 42-V output having a motor/generator and a rechargeable 36-V battery is mounted and which is advantageous in fuel consumption (i.e., so-called 42-V vehicles) is underway. If the above-described power distribution system is applied to this 42-V vehicle, the conversion efficiency is extremely poor, and the generation of large heat entails. This is primarily because the difference between the input voltage value and the output voltage value of the series regulator is large. If the output voltage (i.e., the voltage for the electric load) of the series regulator is specifically assumed to be 5 V, for example, the conversion efficiency of the series regulator in the 14-V vehicle becomes approx. 35.7% from the arithmetic expression (100%xe2x88x92((14 Vxe2x88x925 V)/14 Vxc3x97100%)), whereas the conversion efficiency of the series regulator in the 42-V vehicle becomes approx. 11.9% from the arithmetic expression (100%xe2x88x92((42 Vxe2x88x925 V)/42 Vxc3x97100%)). Namely, if the output voltage at the series regulator is assumed to be fixed, the higher the input voltage at the series regulator, the more the conversion efficiency drops, which causes heat to be generated in various elements in the series regulator. For this reason, it is conceivable to incorporate a switching regulator in each electronic control unit instead of the series regulator as the voltage converting unit exhibiting higher conversion efficiency than the series regulator.
However, in the case of the switching regulator for supplying power to an electric load whose power consumption changes substantially between an active state and a standby state in such as an electronic control unit for a keyless entry system, if the design is made such that the conversion efficiency becomes high when the electric load is heavy (i.e., at the time of the active state when the load current is large), the conversion efficiency at the time when the electric load is light (i.e., at the time of the standby state when the load current is very small) is poor. With such a switching regulator, even in a case where a very small load current (i.e., standby current) is supplied to an electric load in the standby state, there is a large amount of unwanted dark current due to its poor conversion efficiency, which results in large power consumption of the battery and is therefore undesirable. To solve this problem, it is conceivable to provide a power distribution system in which all the electronic control units requiring standby current are provided with a standby-current supplying unit, and power is supplied by the switching regulator at the time when an ignition switch is on (i.e., in the active state), where as power is supplied by a standby-current supplying unit when the ignition switch is off (i.e., in the stand by state).
However, in such a power distribution system, the respective electronic control units need to be provided with expensive switching regulators, and all the electronic control units requiring standby current need to be further provided with the standby-current supplying unit. Therefore, there is a problem in that the power distribution system becomes very expensive.
FIG. 11 shows a power distribution system disclosed in JP-A-10-84626. As shown in FIG. 11, a voltage converting unit 52 is provided in a junction box 51 to which electric power of a high voltage is supplied from a power supply unit 50, this voltage converting unit 52 converts the electric power of a high voltage to electric power of a low voltage (e.g., 5 V), and the electric power of the low voltage is collectively distributed to respective electronic control units 53. According to this power distribution system, since it suffices to provide at least one voltage converting unit 52, it is possible to structure a low-cost power distribution system.
However, in the conventional power distribution system shown in FIG. 11, if power is supplied from the voltage converting unit 52 to distantly located electric loads, a voltage drop is liable to occur, and if consideration is given to the arrangement of the voltage converting unit 52 so that power will not be distantly supplied to electric loads, the number of a voltage converting unit 52 increases and results in higher cost. Furthermore, the voltage converting unit 52 must be designed so that the accuracy of the output voltage, temperature characteristics, and the like of the voltage converting unit 52 conform to the electric load whose requirements are most stringent among the plurality of electric loads. To design the voltage converting unit so as to satisfy the stringent requirements leads to the higher cost of the power distribution system.
Since variations are likely to occur in the output from the voltage converting unit 52 owing to the increase and decrease of the load current, it is difficult to supply electric power of high accuracy to a plurality of electric loads. In a case where power is supplied from the voltage converting unit 52 to an electric load whose power consumption varies substantially between the active state and the standby state as in, for example, the electronic control unit for a keyless entry system or the like, if the design is made such that the conversion efficiency of the voltage converting unit 52 becomes high at the time of the active state when the load current is large, the conversion efficiency at the time of the standby state when the load current is very small is poor. In such a voltage converting unit 52, even in the case where a very small standby current is supplied to the electric load in the standby state, there is a large amount of unwanted dark current due to its poor conversion efficiency, which results in large power consumption of the battery and is therefore undesirable.
The invention has been devised in view of the above-described problems, and its object, among others, is to provide a power distribution system which is capable reducing the unwanted dark current.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A power distribution system comprising:
an upper power distribution unit connected to a power supply unit through a high-voltage power line for receiving power supply of a high voltage from the power supply unit;
a plurality of lower power distribution units connected to the upper power distribution unit through a plurality of intermediate-voltage power lines for receiving from the upper power distribution unit power supply of an intermediate voltage lower than the high voltage, converting the intermediate voltage to a load-use voltage lower than the intermediate voltage and supplying power to electric loads, respectively;
a normal supplying converter provided in the upper power distribution unit for converting the high voltage to the intermediate voltage and supplying the power of the intermediate voltage to the plurality of intermediate-voltage power lines;
a standby-current supplying converter connected in parallel to the normal supplying converter in the upper power distribution unit for converting the high voltage to the intermediate voltage and supplying the power of the intermediate voltage to one of the plurality of intermediate-voltage power lines;
a controller provided in the upper power distribution unit for changing the driving between the normal supplying converter and the standby-current supplying converter;
a master CPU provided in the lower power distribution unit to which power can be supplied from the standby-current supplying converter through the one of the plurality of intermediate-voltage power line, constituting at least a portion of the electric load; and
at least one slave CPU provided in the lower power distribution units other than the lower power distribution unit having the master CPU, constituting at least portions of the electric loads,
wherein the master CPU activates the normal supplying converter in accordance with a predetermined command signal inputted when power is supplied from the standby-current supplying converter to the lower power distribution unit having the master CPU, whereby power is supplied from the normal supplying converter to the plurality of lower power distribution units to drive the electric loads, respectively.
(2) The power distribution system according to (1), wherein the master CPU transmits an activating request signal to the controller to activate the normal supplying converter.
(3) The power distribution system according to (2), wherein the controller transmits an activating completion signal to the master CPU after activating the normal supplying converter, and the master CPU transmits an activating signal to the at least one slave CPU.
(4) The power distribution system according to (1) further comprising a timer circuit which is connected to the master CPU, and stores predetermined time required for the normal supplying converter to reach an active state from a stopped state,
wherein in accordance with a predetermined command signal inputted to the controller and the timer circuit when the standby-current supplying converter is driven, the controller activates the normal supplying converter and the timer circuit counts time until reaching at at least the predetermined time, the timer circuit transmits an activating completion signal to the master CPU after the predetermined time is reached, and the master CPU transmits an activating signal to the at least one slave CPU, whereby power is supplied from the normal supplying converter to the plurality of lower power distribution units to drive the electric loads, respectively.
(5) The power distribution system according to (1), further comprising a comparator provided in the lower power distribution unit having the master CPU for inputting to the master CPU a determination signal representing whether the voltage at the intermediate-voltage power line is a first intermediate voltage or a second intermediate voltage,
wherein the normal supplying converter converts the high voltage to the first intermediate voltage, and the standby-current supplying converter converts the high voltage to the second intermediate voltage different from the first intermediate voltage, and
wherein the master CPU transmits an activating signal to the at least one slave CPU in response to a determination signal of the comparator representing the first intermediate voltage, whereby power is supplied from the normal supplying converter to the plurality of lower power distribution units to drive the electric loads, respectively.
(6) The power distribution system according to (5), wherein the first intermediate voltage is higher than the second intermediate voltage.
(7) The power distribution system according to (1), further comprising: series regulators respectively provided in the lower power distribution units for convert the intermediate voltage to the load-use voltage,
wherein the normal supplying converter has high conversion efficiency of input/output power when the electric load is heavy, whereas the standby-current supplying converter has high conversion efficiency of input/output power when the electric load is light.
(8) The power distribution system according to (1) further comprising a detection sensor for detecting current supplied from the upper power distribution unit to the lower power distribution unit,
wherein the controller stops the standby-current supplying converter and activate the normal supplying converter on the basis of the current value detected by the detection sensor.
(9) The power distribution system according to (8), wherein when an ignition is changed over from off state to on state, the controller stops the standby-current supplying converter and activate the normal supplying converter on the basis of the current value detected by the detection sensor irrespective of the current value detected by the current detection sensor.
The invention has been described briefly above. Furthermore, upon perusal of the embodiments of the invention which are described below with reference to the accompanying drawings, the details of the invention will be clarified further.
The present disclosure relates to the subject matter contained in Japanese patent application No. 2002-012070 (filed on Jan. 21, 2002), which is expressly incorporated herein by reference in their entireties.